We seek to continue our studies of calcium (Ca) changes in spinal cord injury. The proposed experiments are based on our recent findings of large extracellular and tissue Ca changes in cat spinal cords contused by a standard weight drop. The experiments seek to define the relationships of Ca changes with axonal morphology, tissue ATP and phosphate levels, and losses of membrane integrity as demonstrated by axonal uptake of horseradish peroxidase (HRP). A four year study is envisioned. In the first year, we will localize and quantify spinal cord Ca by atomic absorption spectroscopy, ion-selective microelectrodes, and histological methods. In the second year, the measured Ca changes will be correlated with axonal morphology, tissue ATP and phosphate, and distribution of axonal uptake of HRP. In the remaining years, we will investigate a newly discovered phenomenon, that pulse electromagnetic fields (PEMF) specifically alter Ca distribution in injured spinal cords without changing tissue Na, K, or water. The techniques utilized and developed in the preceding two years will be applied to define the specific effects of PEMF on spinal cord Ca, phosphates, ATP, and axonal morphology. By the end of the proposed work, we expect to have determined: (1) the routes and destination of Ca ion shifts in our spinal injury model; (2) the extent to which Ca precipitates with phosphates inside axons; (3) the effect of Ca changes on tissue phosphates and ATP in injured cords; (4) the relationship of Ca accumulation to axonal morphological changes; (5) the proportion of Ca localizing in intact axons not penetrated by HRP; (6) the precise Ca distribution changes produced by PEMF in spinal injury; (7) the acute effects of PEMF on tissue phosphates, ATP, axonal morphology, and HRP uptake by axons in contused spinal cords.